Jan 29, 2015Cooler Heads Will Prevail
With the warmer temperatures of summer just around the corner, it’s never too early to start thinking about strategies to avoid heat illness and dehydration. It’s also a good time to re-examine heat illness and hydration policies, and the data that help you form those policies.
A couple of recent studies indicate that athletic trainers and coaches may need to take a closer look at the available data before making new recommendations to athletes. For instance, an article in the latest issue of the International Journal of Sport Nutrition and Exercise Metabolism indicates that caffeine does not hinder rehydration. According to the researchers’ findings, energy drinks containing caffeine are just as good at hydrating athletes in warm, humid weather as are energy drinks without caffeine.
This theory is supported in an article that recently appeared in T&C that details a study published in 2002 by Lawrence Armstrong, PhD, FACSM, Professor at the University of Connecticut’s Human Performance Laboratory, debunking the dehydration myth.
“We took 59 healthy college males and studied them during 11 days of controlled caffeine intake,” Armstrong says. “One group took no caffeine, a second took three milligrams per kilogram of body mass, and a third took six milligrams per kilogram of body mass. We evaluated them on 20 hydration indices, and the results across all three groups were virtually identical.
“The amount of water retained by the body from a caffeinated beverage is virtually identical to the amount retained from a non-caffeinated beverage,” Armstrong continues. “There is no evidence that caffeine dehydrates the body.”
Sports nutritionists, however, are quick to point out that caffeinated beverages still should not be the hydration source of choice for athletes.
“Dehydration is such a huge issue for student-athletes,” says Leah Moore Thomas, MS, RD, LD, Sports Nutritionist at Georgia Tech, “that the message still needs to be, ‘Caffeine itself may not dehydrate you, but colas and energy drinks are also not designed to properly hydrate you, and they should not be your major source of fluids.'”
In another development on the fluid front, a University of Exeter scientist warns that downing water won’t keep competitors cool in the heat. A recent study published in the Journal of Medicine & Science in Sports & Exercise, says fluid intake has no effect on core body temperature or performance.
Chris Byrne, PhD, a Sport Scientist from the University of Exeter who studied fluid intake in marathon runners said:
“The conventional view among both scientists and the fitness media is that fully replacing sweat losses by fluid intake during exercise will reduce an athlete’s body temperature and improve performance. Our research, which for the first time measured internal body temperature continuously during an actual race, revealed no evidence that fluid intake makes runners cooler or improves performance.”
When athletes are working out in hot weather, warming up should include cooling down. That’s the finding of a study published in the May 2006 edition of the International Journal of Sports Medicine.
“Heat Strain and Gross Efficiency During Endurance Exercise after Lower, Upper, or Whole Body Precooling in the Heat,” can be downloaded for a fee at their Web site. The study, conducted by the Netherlands-based TNO research institute, tested the effect of “precooling,” in this case by having athletes wear special clothing with tubes through which cold water was pumped prior to exercise. Eight male cyclists were asked to ride in summer-like heat after full-body precooling, upper-body precooling, lower-body precooling, and no precooling. Reuters Health summarized the results.
“Compared with the cooling-free ride…the cyclists had fewer signs of heat strain during their [three] post-cooling rides,” the news service reported. “Also, contrary to the researchers’ expectations, precooling the leg muscles did not diminish the athletes’ performance, despite the fact that it’s generally considered a bad idea to work ‘cold’ muscles.”
The concept behind precooling–which can also be performed using cold baths or chilled air–is that if the body is as cool as possible when exercise begins, athletes experience a higher heat tolerance and a lower heart rate. This can decrease their susceptibility to heat strain, especially in conditions of extreme heat and humidity.
Another recent study has found that cross country runners who wore an ice vest during their pre-race warmup experienced a smaller increase in core body temperature during competition than other participants. The study, published in the winter 2006 issue (Vol. 41, No. 4) of the Journal of Athletic Training, followed 18 women from an NCAA Division I cross country team who participated in a race under warm, humid conditions. Nine of the women donned a vest with 22 pouches containing ice packs for an hour immediately before the race, while the other nine wore their normal uniforms. All 18 ingested radiotelemetry sensors to monitor their core body temperature, and readings were taken before and after the race.
Not surprisingly, the vest-wearing athletes had a lower core body temperature at the start of the race, by an average of roughly half a degree Celsius. But the difference was even more pronounced at the finish line: Athletes who had worn the vest experienced an average core temperature increase during the race of 2.12 °C, while the control group experienced an average increase of 2.75 °C.
These results suggest that the cooling benefits of an ice vest can last long after the vest is removed. And a cooler core means a reduced risk of heat stress and other related illnesses, particularly for athletes working out in hot and humid weather.
The performance benefits of a lower core temperature were not examined in this study, but the authors noted that previous research has found pre-cooling to be beneficial only for endurance athletes.
“Generally, performance improvements [have been] observed in studies of endurance events,” they wrote, “whereas performance decrements were observed in short, power events. In the future, researchers will need to determine whether the ice vest has any performance benefits.”
For more information on hydration and cooling practices and products, check out the T&C article: “When It’s Hot.”
In 5 years of monitoring core temperatures in college and professional football players (using the only practical and accurate way – ingested sensors), there is little evidence that pushing fluids is a major factor in keeping body temperature down as Dr. Byrne showed in runners. We have published similar results in football players. As long as cold water is available for ad lib consumptions the players will stay within 2-3% body weight loss which is not detrimental to performance or thermoregulation. Remember – the single most important part of the “water break” is the BREAK itself!!
Sandra Fowkes Godek PhD, ATC,
Department of Sports Medicine
West Chester University